Yeah, e-fans are a venture I wouldn't mind doing on mine either, just a thought on theory of operation.

 

I’m not an engineer or an expert by any stretch, so it is possible that I am mistaken, but this is the basics on how an alternator works.I’m sure that there are a few people here who could give better explanations than this. Most of this information is taken from classes I took years ago and reading on the internet on the subject.


In a nutshell, the basic mechanics of an alternator are thata magnet is spun inside electrical coils. This generates electricity through electro-magnetic-induction. The alternator does not change the mechanical load presented to the drivetrain in order to vary the electrical output. The rotor (the spinning magnet) inside the alternator always weighs the same amount, and presents essentially the same load to the drivetrain regardless of engine speed, orpower demands of the electrical system. The alternator addresses increased power demands by varying the output voltage through the voltage regulator.


An alternator generates A/C electricity, which is rectified into D/C to be compatible with the vehicle’s electrical system. The voltage regulator in the alternator will vary the D/C voltage output depending on the load (the battery and electrical system of the vehicle). When you first start your car the battery will be resting somewhere around 12.6V, so the voltage regulator will output higher voltage (somewhere around 14.4V). Once the battery is near full charge the regulator will reduce output voltage to somewhere around 13.8V which is the float charge voltage for a 12v lead acid battery. The voltage regulator will then vary the voltage output to prevent overcharging the battery.


Check out these articles for a more technical & detailed description. There's also tons more stuff out there if you want to search more.
How Alternators Work | HowStuffWorks
https://en.wikipedia.org/wiki/Alternator_(automotive).



Now if anyone has better information please chime in. I am an advocate for clear and correct information, and have no problem with being corrected with a better explanation.


All that being said, as far as drivetrain power gains from removing the mechanical cooling fan and replacing it with an e-fan, I seriously doubt that you'll gain more than 1-2HP, if that. There are other benefits from the modification that make it worth considering (it's on my list of possibilities), but by it's self it isn't going to have you running a 10 second 1/4 mile.

 

Let me get to a keyboard. Most of that is good info, but I'll clarify why the load increases with increased power draw.

Edit:
I'll go through this a little at a time to cover everything. I originally asked where your info was from to see if the alternator worked in a fancier way than I imagined, but what you said was the basic operation of a AC generator (I'd imagine 3 phase) rectified to DC with some kind of voltage control. I've heard of it being controlled by PWM, but I'm not sure. I'll go over how this works in depth.

So you are correct in the basic construction of the alternator with there being a spinning magnet inside of coils. However, the main drag on the pully, and therefore, drivetrain, is actually the counter-electro-magneto-force. This force is created when a magnetic field passes by a conductor, the coils. The mag field essentially 'pushes' electrons through the wire (in a very predictable way), creating current. Take a look at this awesome vid showing the effects of this force.



The magnet in this vid creates eddy currents in the copper pipe by passing through it. These eddy currents create the counter-electro-magneto-force, which pushes in the opposite direction of the magnetic field that created it. This pushes back on the magnet's falling force, which slows it down. The faster the magnet goes through the tube (or coil), the more force (and current) is generated.

This is mostly true. The main difference is that when the load on your electrical system is increased, it is not the voltage requirement that goes up, but the amperage. Your typical blazer alternator is rated at 105 amps @ ~14V, which, if you do the math, comes out to a maximum power (P=V*A) of ~1470 Watts (just about 2 horsepower 1HP=748W). So if your alternator is 100% efficient (it's not) you will use at most 2HP to run the alt at full draw of 105A. So the load on the alt isn't really the voltage produced, but the amperage, which as I mentioned previously is directly correlated to the drag on the drivetrain through the counter mag force. It's a pretty cool property of electrical systems that makes transformers work the way they do but that's a slightly different process, not much as they work on the same exact principals but whatever.

I truly appreciate your willingness to listen to someone else on something that you may or may not understand fully. This is a pretty complicated thing when you get down to the way electrons behave, way beyond me anyway.

I did mention that I'd say how PWM would control the power system. So PWM (pulse-width-modulation) is a way to control an ON or OFF system with values between the ON and OFF. Like LED dimming. This turns the LED 100% ON and 100% OFF hundreds of times a second to give the overall output of say 50% using the full power only. This can also be used in many other senarios such as car subwoofer amps. If your amp is a Class D amp, it uses PWM to reproduce the sound at a higher level. This control can be used in an alternator to turn the charging ON and OFF very rapidly to create the different levels of power delivery, while the alt is running at a constant speed. This ON and OFF results in an overall power input to the alt that is lower than it would be if it were to be at 100% output all the time without the need for overly complicated control systems.

If anyone has any other questions on this type of thing, I've had schooling for electrical automation and robotics, so I know motors, generators, and complicated electrical systems. I won't say I know much about the blazer specific platform as that requires more specific knowledge, but I can get by with the fundamentals.

 

Good info Thogert. Thanks for sharing it. I love having a better understanding of how things work. I still have a few points that I think I'd like you to clarify further though, if you don't mind.

I'm still not sure I understand from your explanation how the mechanical load is increased when the electrical requirements are increased. The drag caused by the counter-electro-magneto-force is caused and varied by the RPM of the engine, correct? Higher RPM of the magnet will result in a greater counter-electro-magneto-force. How does an increased electrical load cause an increase in the counter-electro-magneto-force?

Does an automotive alternator vary the amperage produced depending on load?

I'm still working on formulating my next couple questions. I'll edit or add another post in a bit.

 

Ahh right, didn't really explain that part did I? I'll have to refresh with my textbook to remember exactly why, but when transformer / generator has a lower resistance on the coils, it allows more current to flow, which I think also creates more of the counter force. This being because as the current increases, the magnitism created in the coils increases, once again, in the opposite direction of the imparting rotational force. I'll look it up to make sure my thoughts are correct on this.

 

Well - alternator load is proportional to demand. Would be nice to know when the electric fans are running at all.

Where I live 8 months out of 12 the temp is low enough that you do not need the fans as soon as you can drive faster than about 25 mph. So load will be minimal on the alternator but the resistance of the viscous coupling always turning the fan will make a difference.

Couple of hp to be gained there.

 

It is true that the viscous coupler will cause the fan to make noise on initial start up then will quiet down fairly quickly when the fluid becomes warm and begins to slip. And unless the radiator alone will not keep up with the cooling requirements, a properly setup electric fan will be dead quiet until requested to turned on. I'd never consider an electric fan as an performance upgrade on a street vehicle. That is unless you are operating out of the "norm" as designed by the engineers. Frankly, the potential of a couple of HP will never be felt in the seat of the pants. I'd stay with the factory fan myself. BTW, I have built cars with computer programmable electric fans so I am not opposed to them in principle.

 

Error 401, part of my electric fan plan is to mount a LED in the dash as close to the temp gauge as I can. That way I can see what temp ( or at least what the gauge reads) my fan comes on and off.

 

Car GENERATORS use magnets, car ALTERNATORS use electromagnets. The alternator field coils create the magnetic field the armature rotates through, creating the electricity. An alternator voltage regulator turns the field coils on and off as needed to produce the correct amount of power needed. When they are off, the drag is reduced, when they are on it is increased.

This higher load is readily apparent if you have ever had an older vehicle where you set the belt tension manually. When the alt belt gets loose, it squeals anytime you add a load, like right after it starts up (replacing the power used by the starter) or turn on the headlights.

 

Nice idea with a control LED.
I will definitively update mine now that I'm building the 4.3l V6. Less mass to spin without the viscous fan. This can add up to 12 - 14 hp when running which is 8 % of my total hp on the 1994 (165 bhp). Now switch the A/C off and you have 10 - 15 % more hp available - how does that sound?

The viscous fans alway have a certain drag and spin all the time. In my climate we only seldom have to use the A/C most of the time it's heating ON. So this upgrades my Blazer. Two fans, variable speed, hooking it to A/C ON and COOLANT TEMP sensors for activation. I have the towing package with large cooling and heat exchangers so the fans may hardly ever run when driving. I expect to see them only in stop-and-go traffic.